1. Field of the Invention
The present invention relates generally to communication among plural nodes, and more particularly, to managing power in a wireless communication network among nodes using frequency hopping radio signals.
2. State of the Art
Communication systems, such as local area networks (LANs), have achieved widespread use for the exchange of information. These systems include a plurality of data processing nodes, or "agents", which contend for access to a communication medium that interconnects the nodes.
Typical communication networks use hardwired interconnections, such as the local area network communication system described in U.S. Pat. No. 4,661,902 (Hochsprung et al). More recent efforts have been directed to developing wireless communication networks. For example, commonly assigned U.S. Pat. No. 5,231,634 (Giles et al) relates to a communication system for regulating communication among a plurality of nodes, each of which is equipped with a radio transceiver. The '634 patent describes medium access control of a wireless LAN to provide decentralized, peer-to-peer access for all of the agents. A peer-to-peer communication system is one in which all agents can freely communicate without any agent having an advantage over another.
Wireless communication systems require consideration of potential problems which do not exist in hardwired systems. For example, in a wireless communication system, the nodes can be mobile, moving in and out of range with other nodes in the system. The '634 patent is directed to continuously ensuring that all agents possess fair access to the communication system (i.e., to avoid, for example, agents which are physically closer to a given destination from having an unfair advantage due to their signal strength being greater than that of agents physically located further from the destination).
Due to their unique considerations, wireless communication systems have not been developed which can exploit communication techniques such as frequency hopping. Frequency hopping is a known spread-spectrum technique whereby a signal is transmitted using a plurality of frequencies. The exact frequency used at any given time is switched from one frequency to another either in a random or a predetermined sequence.
Frequency hopping techniques provide reliable and secure wireless communication. However, conventional frequency hopping techniques are not readily adaptable to a wireless LAN environment, such as the LAN described in the '634 patent. For example, in frequency hopping systems, synchronization among transmitting and receiving stations constitutes a significant problem. In a LAN environment, synchronization becomes a more significant problem since nodes can move into and out of any number of dynamically changing, reconfigurable communication systems, each of which can have an independently synchronized frequency hopping sequence. There is presently no mechanism for establishing and maintaining synchronization among the nodes present in a dynamically changing, reconfigurable communication system.
Further, there is presently no mechanism for optimizing power consumption in a wireless LAN environment. More particularly, although an exemplary node of a wireless communication network can typically provide both transmission and reception functions, there is presently no method or apparatus for reducing power consumption by controlling the transmitter to be powered only during times of actual transmission. In addition, there is presently no method or apparatus for controlling power consumption which permits a receiving node to power off at certain times and yet still receive information from other transmitting nodes within the communication system.